Physiology Flashcards
“gastric receptive relaxation reflex” is another name for this
vaso-vagal reflex
sensory ganglion of CN-X
nodose ganglion
where the afferent & efferent roots of CN-X meet in the brainstem
nucleus tractus solitarius (NTS)
Locations and functions of the submucosal and myenteric plexuses
submucosal = between submucosa and circular muscle (shallower); SENSES LUMEN ENVIRONMENT
myenteric = between circular and longitudinal muscle (deeper); REGULATES CONTRACTION
Primary PSNS and SNS neurotransmitters in the gut
PSNS: ACh
SNS: ACh (pre-ganglionic) and NE (post-ganglionic)
- Any part of the SNS that’s in the GI tract is post-ganglionic and therefore NE
- In the GI tract: both pre- and post-ganglionic PSNS; only post-ganglionic SNS
Which of these are paracrine peptides rather than endocrine hormones?
Gastrin CCK Histamine Secreting Somatostatin GIP
Histamine
Somatostatin
How is the excretion of paracrine peptides different from that of endocrine hormones?
Hormones = secretory granulation Peptides = local diffusion
Where are G cells and what do they secrete?
Stomach; gastrin
Where are I cells and what do they secrete?
Duodenum/jejunum; CCK
Where are S cells and what do they secrete?
Duodenum; Secretin
Which organs secrete GIP?
Duodenum/jejunum
What does Gastrin target and what does it do?
Target: Stomach and Small Intestine
Action: + HCl & Pepsinogen; +Peristalsis
What does Secretin target and what does it do?
Target: Pancreas
Action: + alkaline digestive proenzymes (bicarb) – Peristalsis
What does CCK target and what does it do?
Target: Pancreas & Gallbladder
Action: + bile secretion (relaxation of sphincter of Oddi) and + digestive proenzymes
+ gastric distensibility and - stomach contraction (wants to keep food in the stomach)
What does GIP target and what does it do?
Target: Pancreas & Stomach
Action: + insulin; - peristalsis
What does VIP do?
It is an inhibitory PSNS neurotransmitter (inhibit ACh); decreases constriction of sphincters; increases relaxation; slows everything down so that it can regulate electrolyte fluid balance
Effect of ACh and NE on saliva
Both increase!
What does GRP do?
Increase Gastrin (So increase HCl + Pepsinogen)
What do Enkephalins do?
Inhibit ACh release; inhibits GI motility (opioids)
What does Neuropeptide Y do?
Makes you hungry; relaxes smooth muscle and decreases intestinal secretions
What does Substance P do?
Induces vomiting; contracts smooth muscle
ALWAYS GO WITH ACH
What is the difference between tonic and phasic contractions?
Tonic = constitutively contract without AP input ("below the AP threshold")
Phasic = only contract sometimes; require AP'sWhat is the relationship between a slow wave and an AP?
Slow waves are below the AP threshold; slow waves still involve depolarization and repolarization of the membrane potential
Which cell type stimulates slow waves?
ICC’s
Which part of the brain contains the swallowing center?
Medulla
Which cranial nerves carry afferent input about swallowing?
CN-9 and 10
Which phases of swallowing are under voluntary control?
Only the oral phase
The esophageal phase of swallowing is controlled by both the brainstem swallowing reflex and cells of the ENS. What is the difference between primary and secondary peristaltic waves in swallowing?
Primary – controlled by the medulla. CANNOT OCCUR IF YOU HAVE NO VAGUS NERVE.
Secondary – controlled by the ENS; occur if primary waves don’t clear the esophagus; independent of oral and pharyngeal phases; CAN OCCUR AFTER VAGOTOMY
Describe the pressure differential in the esophagus that occurs with swallowing.
Sphincters = negative pressure when you swallow (they relax and the food gets sucked through)
Length of the esophagus = positive pressure when you swallow
How much of the esophagus is striated (not smooth) muscle?
The upper 1/3 (including and past the UES)
Which hormone upregulates the MMC? What does the MMC do?
Hormone; Motilin (small intestine)
Function: periodic bursting contractions in the stomach q 90 minutes during fasting; they keep food residue from building up in the stomach
Which hormone increases gastric distensibility and decreases gastric contraction (keeps food in the stomach)
CCK
Effect on the rate of gastric emptying:
decreased distensibility of the orad
Increases rate
Effect on the rate of gastric emptying:
Increased tone of the pylorus
Decreases rate
Effect on the rate of gastric emptying:
Decreased force of peristalsis in the antrum
Decreases rate
Effect on the rate of gastric emptying:
Increased diameter and inhibition of segmenting contractions in the proximal duodenum
Increases rate
How long does gastric emptying take?
3 hours
What is the effect of stimulating the entero-gastric reflex?
Decreases rate of gastric emptying (negative feedback from the duodenum)
What is the function of a segmenting contraction?
To grind up food; the predominant contraction type in the intestine
Which muscle types are most important in peristaltic vs segmenting contractions?
Peristaltic – longitudinal
Segmenting – circular
What do ECC’s (entero-chromaffin cells) do?
Secrete 5-HT at IPANs (intrinsic primary afferent neurons); initiate peristalsis
Effect of 5HT on intestinal contractility
+++
Effect of PG’s on intestinal contractility
+++
Effect of insulin on intestinal contractility
+++
Effect of secretin on intestinal contractility
Effect of glucagon on intestinal contractility
Describe the pressure gradient of the internal and external sphincters of the rectum prior to defecation (the rectosphincteric reflex)
IS: negative (relaxed)
ES: positive (contracted) – “holding it”
What happens to the defecation reflex of a patient with a lower spinal cord injury?
Loss of voluntary control (I think the rectosphincteric reflex is still intact)
A deficiency of which neurotransmitter is associated with achalasia? Why?
VIP – decreased relaxation of LES
Destruction of the ENS at the LES would lead to which consequence?
Achalasia
Destruction of the vagus nerve related to diabetes would lead to which consequence?
Gastroparesis
Hirschsprung disease presents with a deficiency of which neurotransmitter?
VIP (since it lives in ganglion cells)
Tonicity of saliva versus plasma: how is the chemical content different?
Hypotonic
HIGHER K/HCO3 (secreted) LOWER NaCl (absorbed)
What are the different functions of ductal and acinar cells in saliva production?
Acinar: make the saliva
Ductal: regulate ion concentration (net absorption)
Which types of GPCR’s regulate PSNS and SNS effects on saliva production?
PSNS = Gq (IP3)
SNS = Gs (cAMP)
*Both increase saliva
Which spinal levels control SNS saliva production?
T1-T3
What effect do Vasopressin & Aldosterone have on saliva?
– NaCl (saving it for the rest of the body)
++ K/HCO3
What are the differences in location and function of the pyloric and oxyntic glands?
Pyloric = antrum; secretes gastrin
Oxyntic = fundus & proximal body; secretes HCl
What do chief cells secrete?
Pepsinogen
What happens to gastrin secretion at low stomach pH?
It is decreased –> less HCl produced (negative feedback)
What does histamine do in the Gi tract?
Potentiates ACh and Gastrin
Giving Atropine (a PSNS blocker) can decrease stomach acid, but it’s not a great treatment. Why?
(*Hint: what are the NT’s used by parietal vs G cells?)
Atropine blocks the direct pathway of HCl secretion (blocks parietal cells from secreting acid).
HOWEVER: it has no effect on G cells (gastrin secretion). This is because the NT at G cells is GRP, not ACh.
Which 2 stomach cell types are directly stimulated by the vagus nerve? What are the NT’s used?
Parietal Cells (ACh) G cells (GRP)
What do D cells do?
Secrete somatostatin
What are the 2 immediate effects of a gastrinoma (ZES)?
+ HCl secretion
+ Parietal cell mass (trophic effect)
Clinical presentation of ZES
Duodenal ulcers with steathorrhea
Why does ZES cause steathorrhea?
Low duodenal pH is a stimulant for pancreatic lipases
Where are gastrinomas (ZES) located?
Pancreas
Effect of H. pylori on HCl levels
DECREASE
Effect of H. pylori on Gastrin levels
INCREASE
Effect of a duodenal ulcer (any type) on HCl levels
INCREASE (drastic in ZE)
Effect of a duodenal ulcer (any type) on Gastrin levels
INCREASE (drastic in ZE)
What are the functions of acinar and ductal cells in the pancreas?
Acinar – secrete enzymes
Ductal – secrete aqueous HCO3
What is the tonicity of pancreatic fluid vs. plasma?
Isotonic (HCO3 secreted = H absorbed)
What happens in the 3 phases of pancreatic secretion?
1- cephalic
2- gastric
3- intestinal
cephalic - initiated by smell and taste; enzymatic secretion (CN-X)
gastric - initiated by stomach distention; enzymatic secretion (CN-X)
intestinal - 80% of all pancreatic secretions! Both enzymatic and aqueous
Which GPCR’s are involved in pancreatic enzyme vs aqueous solution secretion?
Enzymes = I cell –> CCK –> Gq
Aqueous = S cell –> Secretin –> Gs (cAMP)
How does CF lead to pancreatitis?
No HCO3 secretion in intestinal phase = no secretion mechanism for digestive enzymes either
BSEP and MRP-2 both require ATP. In which step of bile synthesis are they involved?
Gallbladder contraction & relaxation of sphincter of Oddi
ASBT is a transporter on enterocytes. In which step of bile acid metabolism is it involved?
Absorption of bile salts into portal circulation by the intestines
NTCP and OATP are both transporters that are involved in re-uptake of recycled bile acids back to the liver. What is the difference between them?
NTCP = sodium dependent OATP = sodium independent
Many parts of the Gi tract participate in passive reuptake of recycled bile acid. Which is the only part with active transporters (ASBT’s)?
Ileum
How much bile acid is recycled?
90%
What effect does an ileal resection have on bile secretion from the intestine?
Greatly decreased, since most active reuptake of bile occurs in the ileum
What effect does SIBO (small intestine bacterial overgrowth) have on bile secretion from the intestine?
Greatly decreased; bacterial can steal bile and eat it; risk factor = high GI pH
Which enzyme is decreased in physiologic jaundice of the newborn?
UDP glucoronyl transferase
Which type of jaundice is caused by anemia?
Unconjugated (back-up)
Which 2 conditions cause conjugated jaundice?
Dubin-Johnson
Rotor
Which type of jaundice is caused by CHF?
Unconjugated (back up)
What are the Folds of Kerckring and what do they do?
Longitudinal folds that increase the SA of the intestine (get shorter as you move through the SI)
Which intestinal cell type is damaged in chemotherapy?
Enterocytes
What do Paneth cells do?
Secrete immune cells in the intestine
Which 2 macronutrients are digested in the mouth?
Carbs & fats
What are the 3 end products of carbohydrate metabolism?
1- glucose
2- galactose
3- fructose
Which form of carbohydrates can be absorbed by enterocytes?
Monosaccharides only
Which two transporters bring monosaccharides into the enterocyte? Which one brings them into the blood?
Apical/luminal = SGLT (glu/gal –2ry active) & GLUT 5 (fru)
Basolateral = GLUT 2 only
Which enzymes break trypsinogen into trypsin? Where?
Enteropeptidase in the SI or
Trypsin in the SI
Where are most proteins absorbed in the Gi tract?
SI
Do amino acids all share the same transporters?
No. On both membranes there are 4 different ones (based on charge)
2 products of trigylceride metabolism
1- monoglyceride
2- fatty acid
2 products of cholesterol ester metabolism
1- cholesterol
2- fatty acid
2 products of phospholipid metabolism
1- fatty acid
2- lysolecithin
How are lipids transported into the blood?
As chylomicrons
Which pathological condition is caused by a deficiency of ApoB, leading to improper chylomicron formation?
Abetalipoproteinemia
B12 metabolism begins with parietal cells in the fundus of the stomach. Where does it end?
Terminal ileum
Autoimmune gastritis causes B12 anemia. What’s another cause of it?
Atrophic gastritis
Na-dependent transporters facilitate absorption of these macros in the small intestine
Water soluble vitamins
The vast majority of electrolyte absorption occurs here
Small intestine
Which 2 electrolytes are secreted in the colon?
1- bicarb
2- potassium
